Max Verstappen was fastest in practice for Formula One's season-opening Bahrain Grand Prix as his Red Bull team immediately lived up to expectations that have soared since testing.
The Dutch youngster, who also topped the time sheets two weeks ago at the same Sakhir circuit with a Honda-powered car that looked stable and quick, set a best time of one minute 31.394 seconds in the afternoon and 1:30.847 in the evening.
Four teams - Red Bull, McLaren, Mercedes and Ferrari - were within four tenths of a second in the more representative second practice with Mercedes-powered McLaren's Lando Norris second and 0.095 slower.
Seven-times world champion Lewis Hamilton was third for Mercedes in 1:31.082.
"It's been alright. A good feeling in the car," said Verstappen, who won the last race of 2020 in Abu Dhabi. "Overall I'm pretty happy.
"I still expect Mercedes to be the strongest Mercedes-powered car."
Valtteri Bottas, who has won the opening race of the championship for the past two years, was second fastest in that session but fifth in the later one when he complained the car was "undriveable" at the end of his last long run.
The Mercedes drivers had struggled with the car's handling in pre-season testing, and particularly the skittish rear end, but seemed to have found more speed and stability in the two weeks since then.
"I think we have taken a step forward but we still have more to do," said Hamilton. "We still have a hill to climb but we're staying positive.
"We thought Red Bull would be as fast as they are, we know they are leading at the moment."
Friday's practice sessions were each one hour long, the format changed since last year when they lasted 90 minutes.
New Ferrari signing Carlos Sainz was fourth fastest in session two, with teammate Charles Leclerc fifth in the earlier one.
Mexican Sergio Perez, Verstappen's new teammate, was sixth and 10th respectively and said he was still getting a feeling for the car.
Australian Daniel Ricciardo, taking Sainz's place at McLaren, was ninth and sixth.
Four-times world champion Sebastian Vettel was 12th and 14th for Aston Martin, after moving from Ferrari, with Canadian teammate Lance Stroll 13th and eighth.
"I feel there's still a lot left on the table just to get used to the car and being able to squeeze the limit," said Vettel.
Twice world champion Fernando Alonso returned after two years out for his first practice session since 2018 and was 15th for Alpine in the second session with the team focusing on aerodynamic developments.
"It felt amazing to be back and you feel different to testing. Racing is racing, and today I had that feeling, so I enjoyed the two sessions so much," said the 39-year-old Spaniard.
Mick Schumacher, son of Ferrari great Michael, ended the day 18th for Haas.
"I felt comfortable in the car, which is a good sign," said the German. "I know there’s a lot to improve from my side still, as a driver I know I have the tools to improve the lap time."